Environment Canada Reverses Siloxane D5 Decision

Nov 1st, 2011 | By | Category: Canada

On October 24, 2011, Environment Canada (EC) released the first independent review of a decision to declare a chemical substance toxic and add it to the List of Toxic Substances maintained pursuant to the Canadian Environmental Protection Act (CEPA). Once added to that list, the government is required to develop risk management tools for the substance, which can include restrictive regulations or an outright ban of the substance’s use in Canada.

Siloxane D5

The decision concerns a substance commonly referred to as Siloxane D5. Its full chemical name is decamethylcyclopentasiloxane. Siloxane D5 is an odorless, colorless liquid that is used in consumer and industrial applications. It is mainly used in blending and formulating personal-care products and cosmetics, and is an intermediate in the production of polydimethylsiloxane silicone polymers. The decision concluded, among other things, that Siloxane D5 did not, and in the foreseeable future will not, pose a danger or risk of harm to the Canadian environment. In effect, it decided, with the benefit of new information not previously available, that the government’s chemical screening assessment came to the wrong conclusion on the environmental risks posed by the substance.


The history of Siloxane D5’s regulatory journey under CEPA moved into the fast lane on January 31, 2009, when EC and Health Canada (HC) released what is known as a final “screening assessment” for the substance. Siloxane D5 is one of 200 chemical substances identified by the departments to be assessed to determine whether it was “toxic” as defined by CEPA. This assessment program was part of the federal government’s overall chemical management plan announced in December 2006 and known as the “Challenge” to industry (to view the Challenge, click here).

In the years leading up to that date, the two departments had conducted an initial screening of all known existing chemical substances in Canadian commerce to identify potential toxicity and develop a list of priority substances for more detailed assessment. The screening assessment for Siloxane D5, which had been prepared in 2008, concluded that, based on the available information, the substance was entering the environment in a quantity or concentration or under conditions that may have an immediate or long-term harmful effect on the environment or its biological diversity.

As a result of that determination, the Minister of Health and the Minister of the Environment recommended that Siloxane D5 be added to the Toxic Substances List in Schedule 1 of CEPA. This decision was based on the potential for harm in the environment; concerns for humans were not identified. One of the affected industry stakeholders, the Silicones Environmental, Health and Safety Council of North America (SEHSC), filed a Notice of Objection on July 10, 2009 pursuant to subsection 332(2) of CEPA.

The SEHSC requested that a board of review be established to inquire into the nature and extent of the danger posed by Siloxane D5 and a related substance, Siloxane D4. The SEHSC claimed that the screening assessments for these substances were not conducted in a manner that was consistent with the best available science and that errors were made in the approach used by government officials when assessing them. Furthermore, the SEHSC stated that new scientific information was available to demonstrate that Siloxanes D4 and D5 did not meet the criteria for toxicity and that new risk assessments should be undertaken. On August 21, 2010, taking into account that new scientific information with respect to Siloxane D5 had been made available since the screening assessment was published in 2008, the Minister of the Environment decided to establish a board of review (the Board) pursuant to subsection 333(1) of CEPA. However, the request with respect to Siloxane D4 was denied. The Minister appointed three expert academic toxicologists to the Board who were mandated by CEPA to conduct an inquiry into “the nature and extent of the danger posed by the substance”.

Over the next 14 months, the Board met with the objectors and a few interested parties to develop procedures and hold a hearing that constituted one of the only boards of review convened under CEPA and the only review of a government decision under the Challenge program.

In the course of doing so the Board had an opportunity to review EC and HC’s methodology in conducting toxicological risk assessments under CEPA and consider the available evidence concerning the likelihood of environmental harm. It also had an opportunity to articulate in its decision the approach such a board of review should take to these reviews in light of the total absence of jurisprudence and little legislative guidance:

“…. the Board interpreted its mandate to mean that it was to inquire into the nature and extent of the risk posed, if any, by Siloxane D5 to the environment and to determine whether detrimental effects were caused or might be caused. In other words, the Board was mandated to conduct what was, in essence, a de novo risk assessment of the substance taking into account all of the available, relevant, scientific information about Siloxane D5.”


The decision provides a detailed overview of how the Board reviewed the environmental risks associated with Siloxane D5 and how EC and HC performed their risk assessments. The Board noted that, in the absence of empirical evidence, EC and HC relied heavily on the use of models and other tools in order to estimate releases of the substance to the environment, as well as its fate and distribution after release. The Board found that these models and tools had several limitations and inaccuracies, which resulted in inaccurate predictions of environmental fates. Faced with more up-to-date predictions of the release and fate of the substance, the Board concluded that smaller amounts of Siloxane D5 were being released to the environment, principally through wastewaters, than predicted by EC and HC.

The Board also considered various processes that would take place in the environment that affected its fate, distribution and bioaccumulation. In this regard, the Board found the government screening assessment lacking and noted that it failed to take into account all of the intrinsic properties of the substance and their effect on fate and transport in the environment and the subsequent exposure to organisms. This failing was, in part, attributed to the application of the regulatory criteria provided under CEPA to determine persistence and bioaccumulation.


At the end of its decision, the Board observed that the government should regularly review its CEPA regulations to ensure that they incorporate up-to-date techniques, methodologies and standards, and should develop guidance documents that provide user-friendly interpretations of how government staff should carry out chemical risk assessments. The same comment applied to government risk assessment models. These tools, it said, should be developed and reviewed in consultation with experts both inside and outside the government, and with stakeholders. The Board also encouraged industry and interested stakeholders to work diligently with government officials when screening assessments are being conducted in order to fill data gaps and provide relevant commentary and analysis. This was clearly a gentle nudge to be more proactive at an earlier stage in the process, in light of the many years that preceded EC and HC’s screening assessment decision and the government calls to stakeholders to provide it with all available information relevant to its risk assessment challenge.

The Siloxane D5 Board of Review decision will no doubt provide much food for thought for the Canadian government, particularly the toxic risk assessment officials at EC and HC. While the Board’s decision does not bind the Minister of the Environment, it is difficult to imagine how he can proceed with the proposed addition of Siloxane D5 to CEPA’s List of Toxic Substances. Other stakeholders in Canada’s Chemical Management Plan now have reason to have faith that if the government does not see the wisdom of their submissions, they may take advantage of a form of appeal by objecting to a decision to add a substance to the List of Toxic Substances and requesting a board of review. Unfortunately, the Minister of the Environment may reject the request. Hopefully, he will see the benefit of the independent expert review provided in the case of Siloxane D5, which may lead to better government decision-making.

More Information

To view the Siloxane D5 Board of Review decision, click here.

About the Author

Robert Fishlock is a Partner in the Toronto, Ontario, Canada law firm of Blake, Cassels & Graydon LLP, where he has provided advice and representation in all areas of environmental law for more than 20 years. His experience includes defending clients charged with air and water pollution, waste management, and worker health and safety offences; defending and pursuing civil claims and government orders for environmental damage and contaminated land; providing advice with respect to environmental permitting, product safety, chemical toxic assessment, transportation of dangerous goods, hazardous waste disposal and recycling and contaminated site clean-up. Robert has appeared before the Ontario Environmental Review Tribunal (and its predecessors) with respect to the issuance of pollution control orders and waste disposal site approvals and before Ontario’s trial and appellate courts with respect to various environmental issues.

Photograph: Canadian Parliament by Nicolas Raymond, Montreal, Quebec, Canada.

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2 Comments to “Environment Canada Reverses Siloxane D5 Decision”

  1. […] This decision was challenged by the Silicones Environmental, Health and Safety Council of North Amer… and requested that a board of review be established to inquire into the nature and extent of the danger posed by D5. […]

  2. Steve Symes says:

    This is a very good article about the potential environmental health effects of this particular siloxane, however, siloxane sure causes a lot of nasty headaches when it goes into landfills and builds up in landfill gas power genrating engines. Surely, this should be considered, as both in Canada and the US there are many people who say that renewable energy production from landfills is the best way to get power (electricity) from waste, and many more landfills are being used to generate lectricity using engines which cost much more to run due to siloxane in the landfill gas. Thanks.

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